Theory of hydrogen pairing in yttrium

The energetics of hydrogen atoms interacting with yttrium have been investigated using the self-consistent cluster model and the local-density approximation. Our results provide a theoretical understanding of a range of novel phenomena observed recently in resistivity, neutron scattering, NMR, and channeling experiments. These include pairing of hydrogen at low temperatures and the pairs' structural origin, the anomalous fast diffusion of hydrogen along the pairing axis compared to the bulk rate, and the lack of long-range order between the pairs in the metal matrix.